Replication and environmental stresses sustained over a cell's lifetime cause damage and ultimately lead to different types of cell death. Understanding the precise molecular mechanisms by which cells age is a major unsolved problem of modern biology. A comprehensive understanding of cellular aging will shed light on chronic diseases such as myeloid cancer and vascular disease, which result from hematopoetic stem cell aging and endothelial cell aging, respectively. Environmental factors have a significant impact on longevity, and one of the best-documented lifespan-extending perturbations is caloric restriction (CR). Yeast, worms, flies, mice, and rats all live longer when reared on CR diets, via a mechanism that remains poorly understood. Genome-scale screens for determinants of the CR response have not been tractable to date; I propose to meet this challenge by harnessing natural genetic variation in the CR response, using wild yeast isolates as a model. My preliminary studies have revealed robust changes between yeast strains in lifespan during CR, including a wild isolate with a distinctly long lifespan under CR conditions. I hypothesize that th genetic determinants of the lifespan extension, growth behavior, and regulatory profile of wild yeast under CR conditions include novel determinants of the CR response. I will test this hypothesis with the following specific aims: Aim 1- I will map the genetic basis of differences between yeast strains in lifespan under CR conditions. Using a panel of genotyped progeny from a cross between two wild yeast isolates, I will assay the lifespan of each with established microfluidic techniques. Statistical-genetic analyses will identify genes and polymorphisms that reproducibly segregate with the lifespan trait, and the role of these factors in lifespan will be validated in independent molecular-genetic experiments. Aim 2- To understand how CR modulates cell proliferation and fitness, I will measure growth traits under CR conditions in the progeny from the cross used in Aim 1, and I will map genetic loci linked to growth behaviors via statistical-genetic methods. Molecular validation of these screen hits will establish genes that mediate the sensing of and response to CR at the cellular level. Comparison to the results of Aim 1 will enable a test of the degree to which lifespan and growth under CR are under shared genetic control. Aim 3- To investigate at a systems level the state of cells grown under CR, I will transcriptionally profile each strain from the cross used in Aim 1. I will map sequence variants that co-inherit with the expression response to CR, and validate these loci in molecular experiments. The results will identify components and connections of the gene network that regulates cell state in response to the nutritional environment, dovetailing with the first two Aim and allowing a genome-scale molecular dissection of growth and longevity decisions during CR.